1. Field of the Invention
The invention relates to a method and apparatus for driving current through a load while protecting the current driver and load from excessive and damaging currents.
2. Description of Related Art
A typical current driver for a load includes a large bipolar or MOS transistor in series with the load such that conduction by the driver transistor causes a certain current to flow through the load. A terminal of the load may be connected to a load voltage V.sub.L, and a terminal of the current driver transistor may be connected to a reference voltage so that the current flows from the load voltage terminal to the reference voltage terminal through the load and the current driver.
The current through the load depends on the fluctuation of the load voltage V.sub.L and reference voltage, the conductance of the load, and the conductance of the current driver.
To protect from excessive and damaging currents flowing through the load and current driver, a current limiting circuit is frequently coupled to the control terminal of the current driver for maintaining a relatively constant current flowing through the load or otherwise for limiting the current flowing through the load. However, when the load fails and becomes a low resistance, or when the power supply fails and provides an excessively high load voltage, it is then desirable that the current driver be completely shut down until the problem is fixed. It is also desirable that normal transient power supply spikes or other normal transient over-current conditions not result in the shutdown of the current driver, since such transient conditions are not damaging to the load.